The glazing on a greenhouse is available in a few different types of materials such as plastics and glass. The important factor to consider when glazing a greenhouse is how light interacts with the glazing material. Incoming light is either reflected, transmitted and/or absorbed depending on the number of layers of glazing material and the surface orientation.
The most common glazing material used in greenhouses is glass, which is installed in a few different methods. Using putty to seal in glass panels is an option; however the putty cracks and deteriorates so this is not an ideal method. Generally the glass panels are secured to plastic strips with metal clips placed at various intervals along the frame. In regions that are prone to high winds, the panes need to be secured with a continuous strip of metal referred to as edge-ridging or bar-capping.
Polycarbonate and Acrylic
Until recently, glass was the most common glazing material used in the construction of a greenhouse. However, with the introduction of polycarbonates, plastics and other alternatives, glass is not the only option anymore. Rigid plastics such as polycarbonate and acrylic cost less than glass and generally last 7 to 20 years. Manufactured in twin-walled sheets with air space between the walls, they act as an insulator. Light transmits through rigid plastics well, but does decrease over time and yellows from the sunlight's UV radiation. Rigid plastics adhere well to a square greenhouse frame, but do not conform easily on curved roofs.
Polythene is a plastic film that is most likely the cheapest material for glazing a greenhouse. However, the durability is not strong in that they only last approximately three to four years. Plastic film is about four to six mils thick and is generally installed in two layers, which are inflated with the use of a small fan. This provides insulation, reduces heat loss and adds strength to the surface of the greenhouse. However, air-inflated greenhouses will suffer 60 per cent more heat loss as compared to glass and rigid plastic, according to Roses, Inc. Some plastic films are available in what is called IR form that aids in reducing heat loss.